1. Field of Invention
The invention relates to photography, and to a film cartridge including an internal mechanisms for extending film from the cartridge through an exit port. More specifically, the invention relates to a film handling device having one mode for thrusting film from a cartridge, and another mode for releasing the film to permit rewinding of the film back into the cartridge.
2. Description of the Prior Art
Most single-spool film cartridges are assembled with a leading end of the film extending through an exit slot in the cartridge shell. This leading end is accessible when the film is loaded in a camera, and is used for threading the film and pulling it incrementally from the shell as exposures are made. When fully exposed, the film is returned to the cartridge by rewinding, including the leading end, to protect the film for removal from the camera. During subsequent processing, the film is released from the cartridge by breaking open the shell. The extended leading end is no longer required for access to the film.
More recent disclosures include single-spool cartridges, sometimes called thrust cartridges, that contain the entire film roll, including the leading end, inside the cartridge shell. Typically the film roll is supported on a spool that is rotated in an unwinding direction to push the film through its convolutions until the leading end is thrust out the exit slot. Internal structures and mechanisms are provided to reduce clock-springing of the convolutions, so the film will follow the intended path without buckling. This approach is used in cameras to access the film, and may be used again during development and printing. The film remains forever attached to the cartridge, or is returned to the cartridge after processing. The cartridge remains intact and is reused for returning the processed film to the customer.
An example of a thrusting film cartridge is disclosed in Robertson et al. U.S. Pat. No. 4,834,306, issued May 30, 1989. According to the Robertson et al. disclosure, film supported on a spool inside a cartridge is rotated in an unwinding direction to extend the film through a cartridge exit slot. Clock-springing is controlled by confining the outermost convolutions of the film to the intended path.